(a) Field of the Invention
The invention relates to ladders and, in particular to a portable, self-adjusting ladder for accessing a flatbed trailer, especially a flatbed trailer for a semi truck.
(b) Description of Prior Art
Flatbed trailers are widely used for transporting machinery, equipment, large articles, and articles in containers. Access to the flatbed is frequently required during loading, unloading and for load inspection or the like. Flatbed trailers are, however, too high for easy access. The average flatbed trailer is about 44-52 inches high, which makes access to the trailer difficult and potentially dangerous. Consequently, ladders have been utilized to permit easy access to a flatbed trailer. Several types and styles of ladder have been designed for use with flatbed trailers. U.S. Pat. No. 5,024,292, which issued Jan. 18, 1991 to Gilbreath et al, and U.S. Pat. No. 3,882,965, which issued May 13, 1975 to Loomis et al, are exemplary of these. Truck ladders that are adjustable in length have also been invented and described in U.S. Pat. No. 4,161,997, which issued Jul. 24, 1979 to Norman, and U.S. Pat. No. Design 359,134, which issued Jun. 6, 1995 to Toews.
Attachments for securing a ladder leaned against a roof or a wall of a building are also described in U.S. Pat. No. 4,311,210, which issued Jan. 9, 1982 to Jackson, and U.S. Pat. No. 4,280,590, which issued Jul. 28, 1991 to Polizzi.
Most of the truck ladders described in the prior art are mounted to the truck or flatbed trailer. While this provides convenient availability, it has several disadvantages. For example, ladders mounted to the trailer are exposed to heavy vibration, corrosive road salts and spray which contribute to wear. Such ladders also generate considerable noise when the trailer is hauled over rough roads. In addition, many truck drivers do not haul the same trailer for an extended period of time. Since a trailer-mounted ladder is not easily moved from one trailer to another, drivers cannot be assured that they will have a ladder with their next load. It is therefore desirable to provide a flatbed ladder which is portable so that it can travel with a driver rather than a specific flatbed trailer. Another disadvantage of the trailer-mounted ladders is their fixed position on the trailer. Certain loads may block access to the trailer simply because they present an obstacle at the location on the trailer where the ladder is mounted.
Another common problem with flatbed trailers is that they are variable in height, because the height of the trailer changes within a limited range when loads are applied or removed. It is therefore desirable to provide a ladder which can be readily adjusted to permit safe access to a trailer, regardless of the load on the trailer.